This invention relates generally to mixing and mass transport. In particular, the invention relates to an apparatus and method for resonant-vibratory mixing.
The mixing of fluids involves the creation of fluid motion or agitation resulting in the uniform distribution of either heterogeneous or homogeneous starting materials to form an output product. Mixing processes are called upon to effect the uniform distribution of: miscible fluids such as alcohol in water; immiscible fluids such as the emulsification of oil in water; of particulate matter such as the suspension of pigment particles in a carrier fluid; mixtures of dry materials with fluids such as sand, cement and water; thixotropic (pseudo plastic) fluids with solid particulates; the chemical ingredients of pharmaceuticals; and biological specimens, such as bacteria, while growing in a nurturing media without incurring physical damage.
Mixing may be accomplished in a variety of ways: either a rotating impeller(s) mounted onto a shaft(s) immersed in the fluid mixture agitate(s) the fluid and/or solid materials to be mixed, or a translating perforated plate does the agitation, or the vessel itself containing the materials is agitated, shaken or vibrated. Mixing may be continuous (as when a rotating impeller is used or the containing vessel is vibrated) or intermittent as when the drive mechanism starts and stops in one or several directions.
With a conventional vibrational mixer, the amplitude can be varied within very narrow limits, and the frequency is generally set at the frequency of the alternating current (AC) power source. Even when using a motor controller with frequency control, the vibrational frequency of a conventional vibrational mixer can be varied only within relatively narrow limits. Mixing at the natural resonant frequency of the mechanism is usually avoided do to the high loads and associated wear of the mechanisms.
When biological tissue is cultivated, all cells must stay suspended in the nutrient broth; that is, the cells should not settle to the bottom of the vessel in which they are cultivated. However, in agitating living cells so as to minimize sedimentation, the mechanical effect of high shear caused by the agitator should not compromise the integrity of the cells. In the case of rotating agitators, quite often the culture medium creates a turbulent vortex into which the cells are sucked. Under the turbulent vortex conditions, the cells are at greater risk of being mechanically damaged and the continuous supply of oxygen to the cells is not consistently assured.
The background art is characterized by U.S. Pat. Nos. 2,091,414; 3,162,910; 2,353,492; 2,636,719; 3,498,384; 3,583,246; 3,767,168; 4,619,532; 4,972,930; 5,979,242; 6,213,630; 6,250,792; 6,263,750; and 6,579,002; the disclosures of which patents are incorporated by reference as if fully set forth herein.
Newport et al. in U.S. Pat. No. 2,091,414 disclose an apparatus for effecting vibration. This invention is limited in that only a single-mass system is disclosed.
Behnke et al. in U.S. Pat. No. 3,162,910 disclose a apparatus for shaking out foundry flasks. This invention is limited in that only a single-mass system and a single set of springs is provided.
The present invention overcomes the limitations of U.S. Pat. Nos. 2,353,492 and 2,636,719 issued to John C. O'Connor (the “O'Conner patents”) and U.S. Pat. No. 6,213,630 issued to Olga Kossman (the “Kossman patent”). The O'Conner patents disclose devices, which provide for the vibrational compaction of dry materials and for the feeding of material via a vibratory conveyance. The Kossman patent claims electronic control of motors for the purpose of vibrational control of a compaction device.
The O'Conner patents disclose vibrational mechanisms comprised of two masses. A means of imposing a cyclical force is attached to the first mass. The second mass, which holds or includes the material to be affected, is resiliently mounted to the first. The assembly is then held by resilient members to a fixed ground position. This mechanism can be effectively tuned by proper resilient member selections to substantially reduce transmitted forces to the ground position but is limited in its ability to reduce accelerations imposed on the first mass. Accelerations on the first mass, which includes the driver inducing the cyclical forces, induce high forces which in turn lead to premature failures. To lower the failure rates of the driver, either the induced forces must be reduced or the mass of the material to be affected must be severely limited. Both cases limit the available applications of the device. Further, it is stated that the preferred operating conditions are between the first and second modes of peak vibrations. This further limit the device's effectiveness due to the additional power required to operate in this range for optimum mixing accelerations and amplitudes. If the device were to operate at one of the peek modes only enough power to overcome inherent damping of the device would be required to effect maximum acceleration and amplitude at mass two.
The Kossman patent discloses a method of controlling the driver motor or motors of a vibrational device similar to the O'Conner patent. The desclosed device lacks the ability to operate at the natural frequency peaks and also suffers from a lack of ability to limit transmitted forces to either the driver or ground positions.
Ogura in U.S. Pat. No. 3,498,384 discloses a vibratory impact device. This invention is limited in that only a two-mass system is disclosed. It is not possible to achieve high payload accelerations, force cancellation and low driver accelerations with a two-mass system.
Stahle et al. in U.S. Pat. No. 3,583,246 disclose a vibration device driven by at least one imbalance generator. This invention is limited in that only a single-mass system is disclosed.
Dupre et al. in U.S. Pat. No. 3,767,168 disclose a mechanical agitation apparatus. This invention is limited in that only a single-mass system is disclosed.
Schmidt in U.S. Pat. No. 4,619,532 discloses a shaker for paint containers. This invention is limited in that only a double-mass system is disclosed.
Davis in U.S. Pat. No. 4,972,930 discloses a dynamically adjustable rotary unbalance shaker. This invention is limited in that only a single-mass system is disclosed. Moreover, the vibratory driver is directly attached to the single mass and this mass is attached to ground by pneumatic springs. High driver accelerations are an unavoidable result of such a device.
Hobbs in U.S. Pat. No. 5,979,242 discloses a multi-level vibration test system having controllable vibration attributes. This invention is limited in that it discloses a multi-driver system with a driver attached on each of the masses in the system. No disclosure of means for achieving low driver accelerations or low transmitted forces to ground is made.
Krush et al. in U.S. Pat. No. 6,250,792 discloses an integrated vibratory adapter device. This invention is limited in that only a single-mass system is disclosed.
Maurer et al. in U.S. Pat. No. 6,263,750 disclose a device for generating directed vibrations. This invention is limited in that only a single-mass system is disclosed.
Bartick et al,. in U.S. Pat. No. 6,579,002 disclose a broad-range large-load fast-oscillating high-performance reciprocating programmable laboratory shaker. This invention is limited in that only a single-mass system is disclosed. This invention is not capable of operating in a resonant condition as it is displacement rather than vibration driven.
In summary, the background art does not teach a three-mass system having a structure that is capable of achieving low-frequencies of 0–1000 Hertz (Hz), high accelerations of 2–75 accelerations equal to that caused by gravity (g's) and large displacement amplitudes of 0.01–0.5 inches. What is needed is an apparatus and method for mixing fluids and/or solids in a manner that can be varied from maintaining the integrity of fragile molecular and biological materials in the mixing vessel to homogenizing heavy aggregate material by supplying large amounts of energy.